Wireless radio transmission systems can be configured on the basis of transmitters and receivers capable of transmitting and receiving modulated data signals in the form of, for example, single carrier or multiple carrier data signals. One example of a multiple carrier radio transmission system is Orthogonal Frequency Division Multiplexing (OFDM) in which an OFDM transmitter broadcasts information consisting of symbols containing a plurality of equally spaced carrier frequencies. The characteristics of the wireless communication channel typically vary over time due to changes in the transmission path. For demodulating OFDM modulated data in the presence of substantial time variations of the transmission channel, knowledge of the transmission channel frequency response is required. This necessitates that the receiver provides an appropriate channel estimate of the transmission channel.
In wireless radio transmission systems a transmitted signal reaches a receiver after propagation through a wireless communication channel. In the propagation channel, the transmitted signal interacts with the environment in a very complex way. The signal propagation through a wireless communication channel causes various types of impairment in a received signal due to reflections from large obstacles, diffraction around smaller objects and edges, and refraction through the medium and signal scattering. These complex interactions result in reception of multiple delayed versions or replicas of the transmitted signal through multiple paths with each version having randomly distributed amplitude and phase. In general, a channel is known to experience a delay spread or a time dispersion due to multiple paths and is referred to as a multipath fading channel.
Multipath fading may cause errors in signal decoding due to inter-symbol-interference (ISI) and may further affect the performance of communication systems. Therefore, the delay spread is considered to be one of the important characteristics of propagation channels since it affects the performance of the communication systems. However, an even more important characteristic of the propagation channel is the exact placement of the delays within the window. Therefore the knowledge about the delay paths of a channel can thus be used for designing a better receiver structure which can adapt itself to deal with the changing nature of the underlying channel and provide an improved performance that enhances the user experience.
Conventional methods for delay estimation and path finding are not able to achieve the necessary time resolution which means that paths which are relatively near to each other in time cannot be resolved in time in a satisfying way. Other known methods may be able to reach a satisfying time resolution but may require optimization in dimensions on the order of the number of paths which could mean, for example, a 6-dimensional optimization problem which would require a large computational complexity.